[OLPC library] [OLPC-Games] Physics -- Newtonian mechanics.. for kids!

[Edward Cherlin]

On Sat, Jul 12, 2008 at 1:21 PM, Yoshiki Ohshima <yoshiki at vpri.org> wrote:
> At Thu, 10 Jul 2008 16:58:32 -0700,
> Edward Cherlin wrote:
>>
>> On Thu, Jul 10, 2008 at 4:20 PM, Yoshiki Ohshima <yoshiki at vpri.org> wrote:
>> >> So we could simulate a pendulum or a Newton's cradle? How do you
>> >> handle collisions?
>> >
>> >  A pendulum for sure, but my version of three pendulums putting
>> > together doesn't show the expected behavior.  The elasticity isn't
>> > right for it, it seems.
>>
>> What does it do? Can you get it to tell you what values of momentum
>> and energy are passed through from balls 1-->2-->3?
>
>  Heh, of course you can try by yourself.

I want to know what happens in your code. Can you send it to me?

>  But if you put a circle on
> the floor (stand still), and make another hit from the side, the
> momentum is shared by these two circles and both of them move together
> at the same speed.

That's unphysical, and I would only program that way in a fantasy
setting. In a head-on elastic collision of two circles of equal mass,
the hitter should stop dead, transferring all of its energy and
momentum to the one it hit. As any pool payer knows for the case of
spheres. In a Newton's cradle the momentum and energy passes from ball
to ball at the speed of sound in the material of the balls.

>> Have you tried two pendula hanging from a horizontal string? Do you
>> get the expected transfer of energy back and forth?
>
>  Yes, but no.  I'm not sure what you mean by a horizontal string, but
> the string I made is not flexible enough to make it happen.

Tie a string between two points at the same height.

Then tie a pendulum to the string.

Then tie another pendulum of the same length and mass to a different
point on the string.

   \____/
    |       |
   o      o

Start one pendulum in the direction perpendicular to the plane of the
diagram. It will gradually transfer energy and momentum to the other
almost completely, and then start up again while the other slows down
and stops, and so on.

>  Speaking of examples, the screenshots at
> http://wiki.laptop.org/go/Physics_(activity) aren't exactly something
> I found "physics-y"; these are more like story telling in picture
> books.  I made some examples (two pendula and a mesh, I did an arch
> but it is gone).  These might catch more attention from teachers and
> educators.
>
> -- Yoshiki
>
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-- 
Edward Cherlin
End Poverty at a Profit by teaching children business
http://www.EarthTreasury.org/
"The best way to predict the future is to invent it."--Alan Kay